Don Stauffer
I also remove tape soon after painting.
I've left my waterline masking in place a week or more with no ill effects.
My painting method is to first freehand paint a broad black belt around the waterline. Once it dries I mask using 3M vinyl auto painters pin striping tape. It bends and conforms well to compound curves like under the stern. Burnish it down well. This tape isn't for finish pin stripes, rather its used to define edges for custom flames, scallops, and the like. Its available in varying widths from auto body & paint supply shops.
I then paint the underhull. When that dries I mask the underhull, running the masking tape (3M blue painters tape, Frog Yellow or Frog Green) up onto the vinyl pin stripe tape. Do not run the masking over the top edge of the vinyl tape.
Then I paint the upper hull. It may be in several steps to paint the deck.
Once the upper paint is dry I remove all the masks and have a straight boot topping separating the red underhull from the gray upper hull. Now this may have taken me more than a week to complete allowing for work schedules, honey-do projects, and drying time. I've had masking wait up to a month for removal. The flexible vinyl tape may be the key.
You need to practice and find a method which works for you.